OpenStem

@openstem · Joined Jul 2026

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Note~290 words · 1 min

Chemical Symbols Every element has its own shorthand code called a chemical symbol — one or two letters that chemists everywhere understand, no matter what language they speak. Notice the pattern: a symbol with two letters always has a capi

Chemistry

Chemistry · L2 · Elements, Compounds & Chemical Formulae

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Note~457 words · 2 min

Solubility and Solutions When a solid, liquid, or gas dissolves completely into a liquid, the result is called a solution. The substance that dissolves is the solute, and the substance that does the dissolving is the solvent. Stir a spoon o

Chemistry

Chemistry · L2 · Solubility and Solutions

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Note~368 words · 2 min

Combustion and Fuels Combustion is the scientific name for burning. It is a chemical reaction between a fuel and oxygen that releases heat and light — and, like all chemical changes, it makes brand-new substances that cannot easily be turne

Chemistry

Chemistry · L2 · Combustion and Fuels

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Note~271 words · 1 min

Reading Hazard Symbols Chemical containers and lab bottles carry hazard pictograms — small pictures inside a diamond or square that warn you what kind of danger is inside, before you even open the label's fine print. A container can show mo

Chemistry

Chemistry · L2 · Chemical Safety and Hazard Symbols

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Note~310 words · 2 min

Energy in Chemical Reactions Every chemical reaction involves a change in energy, not just a change in substances. Some reactions release energy into their surroundings, and some reactions absorb energy from their surroundings. You can ofte

Chemistry

Chemistry · L2 · Energy in Chemical Reactions

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Note~411 words · 2 min

Every Acid Reaction Makes a Salt You already know acids from bases by their pH. What matters now is what happens when an acid actually reacts with something: it almost always forms a salt. A salt is a compound made when the hydrogen in the

Chemistry

Chemistry · L2 · Making Salts

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Note~434 words · 2 min

Metal + Acid → Salt + Hydrogen As you saw in the reactivity series, a reactive metal added to an acid fizzes — sometimes fast, sometimes slowly. That fizzing is a real chemical reaction, and it always follows the same pattern: the metal dis

Chemistry

Chemistry · L2 · Metals Reacting with Acids

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Note~561 words · 3 min

Four Gases, Four Tests Chemists often need to identify an unknown gas quickly, without any fancy equipment. Over time, four simple tests have become standard — one for each of the gases you meet again and again in the lab: oxygen, carbon di

Chemistry

Chemistry · L2 · Testing for Gases

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Note~299 words · 1 min

Fermentation: Living Yeast Without Oxygen Yeast is a living microorganism — far too small to see, but very much alive. Most living things need oxygen to release energy from food. Yeast can do something different: when there is no oxygen aro

Chemistry

Chemistry · L2 · Fermentation

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Note~597 words · 3 min

Protecting Metal Structures — Beyond Paint and Galvanizing A coat of paint or a galvanized zinc layer is enough to protect a garden fence or a box of nails. But ships, oil pipelines, and bridges are huge, expensive, and exposed to some of t

Chemistry

Chemistry · L2 · Protecting Metal Structures

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Note~457 words · 2 min

Energy in the Water Cycle You already know that a chemical reaction can be exothermic — releasing energy and getting warmer — or endothermic — absorbing energy and getting colder — and that a simple touch test on the container can tell you

Chemistry

Chemistry · L2 · Energy in the Water Cycle

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Note~576 words · 3 min

What Is an Alloy? An alloy is a mixture of a metal with one or more other elements — often another metal, sometimes a non-metal like carbon. Metals are usually melted and stirred together, then left to cool and solidify as one solid mixture

Chemistry

Chemistry · L2 · Alloys — Mixing Metals for a Purpose

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Note~419 words · 2 min

Energy Stored in Chemical Bonds You already know that an exothermic reaction releases energy and warms its surroundings, while an endothermic reaction absorbs energy and cools its surroundings. But where does that energy actually come from,

Chemistry

Chemistry · L2 · Energy Stored in Chemical Bonds

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Note~477 words · 2 min

Nature's Own pH Indicators You already know that litmus paper and universal indicator change colour to show acid or base. It turns out some plants make their own colour-changing pigments too — no laboratory required. Red Cabbage Juice — A H

Chemistry

Chemistry · L2 · Natural pH Indicators

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Note~550 words · 3 min

What Is Gas Pressure, Really? A gas is made of an enormous number of tiny particles, spread far apart and moving around constantly in every direction. They are far too small and far too fast to see individually, but together they do somethi

Chemistry

Chemistry · L2 · Gas Pressure — the Particle Picture

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Note~766 words · 4 min

What Comes Out of a Flame Every day, all sorts of fuels burn around us — a candle flame, a gas hob, a car engine. Whatever the fuel, burning always makes something. This page compares what actually comes out of the flame for several differe

Chemistry

Chemistry · L2 · What Comes Out of a Flame

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Note~429 words · 2 min

From River to Tap: Treating Water for Drinking Water taken from a river or reservoir is not safe to drink straight away. It can carry floating rubbish, suspended grit, and microscopic pathogens. A water treatment plant cleans it up through

Chemistry

Chemistry · L2 · Treating Water for Drinking

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Note~431 words · 2 min

Getting Metals from Ores Metals don't arrive ready to use — they have to be got out of the ground first. Exactly how depends on one thing: where the metal sits in the reactivity series. The more reactive a metal is, the more tightly it hold

Chemistry

Chemistry · L2 · Getting Metals from Ores

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Note~440 words · 2 min

Fibers and Fabrics for Clothing Every piece of clothing is woven or knitted from fibers — thin strands of material spun into thread. Some fibers are grown by plants and animals; others are manufactured in factories. Choosing the right fiber

Chemistry

Chemistry · L2 · Natural and Synthetic Fibers

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Note~473 words · 2 min

How Batteries Work A simple battery can be made from two DIFFERENT metals — like zinc and copper — both dipped into an electrolyte: a liquid that can carry a charge. Salty water works, lemon juice works, and even the juice inside a potato w

Chemistry

Chemistry · L2 · How Batteries Work

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Note~518 words · 3 min

The Carbon Cycle You've already seen that burning a fuel like methane produces carbon dioxide and water, and that carbon dioxide makes up a tiny slice of the air — about 0.04% of it. This page ties those two facts together into a single loo

Chemistry

Chemistry · L2 · The Carbon Cycle

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Note~542 words · 3 min

How Soap Is Made You already know that a soap molecule has two ends — one that loves water and one that loves grease — and that this is what lets soap wash grease away. But where does that molecule actually come from? Soap is not dug up or

Chemistry

Chemistry · L2 · How Soap Is Made — Saponification

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Note~437 words · 2 min

Old Tricks That Still Work Long before anyone knew that bacteria and mould existed, people were already preserving food with salt, vinegar, and sugar. These methods survived for thousands of years simply because they worked — even though no

Chemistry

Chemistry · L2 · The Chemistry of Food Preservation

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Note~537 words · 3 min

What Makes a Dissolved Substance an Electrolyte? Not every dissolved substance behaves the same way once it is in water. Some substances, like table salt, split apart into separate charged particles called ions as they dissolve. Those ions

Chemistry

Chemistry · L2 · Electrolytes and Sports Drinks

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Note~767 words · 4 min

Electrolysis: using electricity to force a reaction A galvanic cell takes a spontaneous redox reaction and lets it generate an electric current. Electrolysis runs the idea in reverse: it takes an electric current from an external supply and

Chemistry

Chemistry · L3 · Electrolysis

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Note~801 words · 4 min

Which reactant runs out first? Stoichiometry lets you convert between mass, moles, and mole ratios for a single reactant. Real reactions usually start with TWO reactants measured out independently, and they rarely arrive in exactly the rati

Chemistry

Chemistry · L3 · Limiting Reagents and Percent Yield

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Note~676 words · 3 min

From percent composition to a ratio of atoms Stoichiometry gave you a one-step conversion: mass to moles, using n = m/M. Empirical formula work uses that exact same conversion three times in a row — once per element — and then compares the

Chemistry

Chemistry · L3 · Empirical and Molecular Formula

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Note~59 words · 1 min

From structure to reaction Ethanol is a small molecule — two carbons, an oxygen, and some hydrogens: When a fuel like methane burns in oxygen, it produces carbon dioxide and water. The equation is balanced — the same atoms appear on both si

Chemistry

Chemistry · L3 · Molecules and Reactions

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Note~301 words · 2 min

One string, one reaction A SMILES string normally names a single molecule. Add a '>' and it names a whole reaction: reactants, then reagents, then products. Nothing else changes — the notation carries the meaning. Here bromomethane meets a

Chemistry

Chemistry · L3 · Reading reactions in SMILES

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Note~452 words · 2 min

Inside the atom Every atom is built from three subatomic particles. Protons carry a positive charge and neutrons carry no charge at all — both are packed tightly together in the nucleus, the small, dense centre of the atom. Electrons carry

Chemistry

Chemistry · L3 · Atomic Structure & Electron Shells

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